A vehicle is generally equipped with a radiator to improve cooling efficiency of a coolant for cooling the engine of the vehicle and a cooling fan to accelerate cooling of the coolant passing through the radiator. The cooling fan is connected with a fluid fan clutch, which receives power transferred via a water pump pulley of the engine and transfers the power to the cooling fan to rotate the cooling fan when the temperature of the radiator is high. The fluid fan clutch is provided with an actuator causing introduction of a viscous fluid. Hereinafter, a conventional actuator will be described in detail with reference to accompanying drawings.
FIG. 1 is a cross-sectional view of a conventional electronic actuator for a fan clutch.
The conventional electronic actuator is formed to generate electric lines of three and is provided with a bearing installed therein. Specifically, FIG. 1 is a cross-sectional view of a viscous fluid clutch actuator, which is a conventional technology disclosed in U.S. Pat. No. 6,557,686 B1 (May 6, 2003). The actuator 10 includes a housing 14, a shall 16, a nut 18, a nonmagnetic bushing 20, a bearing 22, an electrical coil 24, and a ferromagnetic can 26. The rotary shaft 16 includes a first end portion 2$ and a second end portion 30. The first end portion 28 is disposed outside the housing 14, and the second end portion 30 is disposed inside the housing 14 such that the shaft 16 rotates easily in the housing 14. The nut 18 includes an inner peripheral surface 32, an outer peripheral surface 34, and a fastening means 36. The fastening means 36 is adapted to attach the actuator 10 to the clutch 12. When the actuator 10 is attached to the clutch 12, the nut 18 spins with the clutch 12. The stainless steel bushing 20 is adapted to couple the first end portion 28 of the shaft 16 and the inner peripheral surface 32 of the nut 18.
Accordingly, the shaft 16, the hearing 22, and the nut 18 integrally spin with the clutch 12. In addition, the bearing 22 is disposed around the second end portion 30 of the shaft 18 and is adapted to facilitate rotation of the shaft 16. The ferromagnetic can 26 is disposed in a ring shape around the shaft 16. The electrical coil 24 is disposed in the ferromagnetic can 26. The bearing 22 is disposed outside the ferromagnetic can 26 such that a magnetic flux loop 48 is formed inside the bearing 22.
According, to the conventional technology configured as above, when power is applied to the electrical coil 24, the magnetic lines of force 48 are produced through a magnetic body around the coil. The magnetic lines of force 48 produce magnetic force in an air gap present in an armature plate 42. The magnetic force pulls the armature plate 42 inward, from a spring-loaded closed position to an open position. In the open position, the armature plate 42 allows viscous fluid flow and coupling within the clutch 12. In this manner, the actuator 10 actuates the clutch 12. In this manner, the actuator 10 actuates the clutch 12.
However, in the case of the conventional electronic actuator configured for a fan clutch as above, the density of the magnetic lines of force 48 is relatively low and thus the force pulling the armature plate 42 is weak. Moreover, as the bearing 22 is disposed outside the ferromagnetic can 26, shaking of the shaft 18 may be amplified to increase unbalanced load applied to the hearing 22. In addition, since the internal structure of the actuator 10 is complex, compact design of the fan clutch is restricted and the manufacturing costs increase.